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Pseudomonas aeruginosa SeMet-PilM bound to ADP
Structural highlights
FunctionPILM_PSEAE Inner membrane component of the type IV (T4S) secretion system that plays a role in surface and host cell adhesion, colonization, biofilm maturation, virulence, and twitching, a form of surface-associated motility. PilN/PilO heterodimers form the foundation of the inner-membrane PilM/PilN/PilO/PilP complex which plays an essential role in the assembly of a functional T4 pilus (PubMed:19857645, PubMed:19857646). In turn, associates with PilN and facilitates PilM functionally relevant structural changes that differentially impacts PilM binding to PilB, PilT, and PilC (PubMed:27022027).[1] [2] [3] Publication Abstract from PubMedPseudomonas aeruginosais an opportunistic bacterial pathogen that expresses type IVa pili (T4aP). The pilus assembly system, which promotes surface-associated twitching motility and virulence, is comprised of inner and outer membrane subcomplexes, connected by an alignment subcomplex composed of PilMNOP. PilM binds to the N-terminus of PilN, and we hypothesize that this interaction causes functionally significant structural changes in PilM. To characterize this interaction, we determined the crystal structures of PilM and a PilM chimera where PilM was fused to the first twelve residues of PilN (PilM:PilN1-12). Structural analysis, multi-angle light scattering coupled with size exclusion chromatography, and bacterial two-hybrid (BACTH) data revealed that PilM forms dimers mediated by the binding of a novel conserved motif in the N-terminus of PilM, and binding PilN abrogates this binding interface resulting in PilM monomerization. Structural comparison of PilM to PilM:PilN1-12 revealed that upon PilN binding there is a large domain closure in PilM that alters its ATP binding site. Using biolayer interferometry we found that the association rate of PilN to PilM is higher in the presence of ATP compared to ADP. BACTH data suggested the connectivity of the cytoplasmic and inner membrane components of the T4aP machinery inP. aeruginosa, with PilM binding to PilB, PilT, and PilC, in addition to PilN. Pull-down experiments demonstrated direct interactions of PilM with PilB and PilT. We propose a working model in which dynamic binding of PilN facilitates functionally relevant structural changes in PilM. PilN binding modulates the structure and binding partners of the Pseudomonas aeruginosa Type IVa Pilus protein PilM.,McCallum M, Tammam S, Little DJ, Robinson H, Koo J, Shah M, Calmettes C, Moraes TF, Burrows LL, Howell PL J Biol Chem. 2016 Mar 28. pii: jbc.M116.718353. PMID:27022027[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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